Method for detecting a moving object in motion video and apparatus therefor

ABSTRACT

An apparatus for detecting a moving object in motion video comprises a macro-block determining section for determining the background/non-background of each macro-block of a reconstructed video signal from a video decoder section which decodes encoded data obtained by compression-encoding a motion video signal, a moving object determining section for determining an area of the moving object from the result of the determination on the background/non-background, and a moving object combination display for displaying information indicating the area of the moving object on a display screen for the reconstructed video signal. The macro-block determining section determines if a macro-block represents a background area or a non-background area, based on mode information from the video decoder section and a cross correlation value between a present frame of the reconstructed video signal and a signal of a frame preceding the present frame by one frame, obtained by a first cross correlation calculator, and a cross correlation value between the present frame of the reconstructed video signal and a background video signal stored in a background memory, obtained by a second cross correlation calculator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 11-248851, filed on Sep. 2,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for detecting a moving objectin motion video and an apparatus therefor, and, more particularly, to amethod for detecting a moving object in motion video from the output ofa video decoder and an apparatus therefor.

To detect a moving object present in motion video, it is generallynecessary to check the motion of each pixel image. But, thepixel-by-pixel motion checking actually requires a vast amount ofcomputation. In the case of the CIF format that is often used in H.261or H.263 in ITU-T which is the international standard for videocompression, MPEG-4 or the like of ISO/IEC, for example, it is necessaryto detect the motion of each of a huge number of pixel images amountingto 101,376 pixels consisting of 352 pixels horizontal by 288 pixelsvertical. Such a process that demands a vast amount of computation needsspecial hardware, which leads to an increased cost.

Jpn. Pat. Appln. KOKAI Publication No. 252467/1997 proposes a movingobject detecting apparatus which employs a scheme of detecting a movingobject from the motion vector that is generated by a video encoder. Asthis scheme can use a motion vector for each block generated by thevideo encoder in detecting a moving object, it need not to particularlycheck the motion of each pixel in order to detect a moving object. Thisscheme can significantly reduce the amount of computation needed todetect a moving object.

However, a block which shows a large motion vector or a rewritten blockshould not necessarily be a moving object. Further, a block which hasnot been rewritten may be present even in a block in a moving object. Inconsideration of adapting the moving object detecting method, which usesthe aforementioned motion vector, to monitoring a moving object, thismethod may not be able to acquire needed videos.

As apparent from the above, the prior art requires a vast amount ofcomputation to detect a moving object so that the conventional methodthat uses encoded video data does not provide a sufficient precision.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a videomoving object detecting apparatus capable of detecting a moving objectfast, stably and accurately.

According to a first aspect of this invention, there is provided a videomoving object detecting method comprising the steps of determining if avideo signal in a given unit area (e.g., a macro-block) represents abackground area or a non-background area from a reconstructed videosignal acquired by decoding encoded data obtained bycompression-encoding a motion video signal; and determining an area of amoving object from a result of the determination on whether the videosignal represents the background area or the non-background area. Thismethod further includes a step of displaying information indicating thearea of the determined moving object on a display screen for thereconstructed video signal.

According to a second aspect of this invention, there is provided avideo moving object detecting apparatus comprising abackground/non-background determining section for determining if a videosignal in a predetermined unit area of a reconstructed video signalacquired by a video decoder section for decoding encoded data obtainedby compression-encoding a motion video signal represents a backgroundarea or a non-background area; and a moving object determining sectionwhich determines an area of a moving object from a result of thedetermination done by the background/non-background determining sectionfor each unit area. The video moving object detecting apparatus furthercomprises a display section which displays information indicating thearea of the moving object, determined by the moving object determiningsection, on a display screen for the reconstructed video signal.

More specifically, the video moving object detecting apparatus accordingto this invention further comprises a first cross correlationcomputation section which computes a cross correlation value between apresent frame of the reconstructed video signal and a signal of a framepreceding the present frame by one frame, unit area by unit area; astorage section for storing a background video signal indicative of abackground portion of the reconstructed video signal; and a second crosscorrelation computation section which computes a cross correlation valuebetween the present frame of the reconstructed video signal and thebackground video signal stored in the storage section, unit area by unitarea, wherein based on mode information indicating an encoding modeacquired from the video decoder section and the cross correlation valuesacquired by the first and second cross correlation computation sections,the background/non-background determining section determines if thevideo signal in the predetermined unit area represents a background areaor a non-background area.

The video moving object detecting apparatus further comprises an updatesection which, when the background/non-background determining sectiondetermines that the video signal in the predetermined unit area of thereconstructed video signal represents a background area, updates thebackground video signal stored in the storage section with the videosignal in the unit area which has been determined as representing thebackground area.

The moving object determining section determines, as the area of themoving object, an area where, for example, a plurality of unit areaswhich have been determined as representing a non-background area by thebackground/non-background determining section are located adjacent toone another.

In short, because this invention can further determine what lies insidea moving object or the background hid behind the moving object bycombining the video decoding scheme with detection of a moving object,the invention can detect a moving object in motion video fast with asmaller amount of computation, stably and accurately.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a block diagram illustrating the structure of a video movingobject detecting apparatus according to one embodiment of thisinvention;

FIG. 2 is a flowchart schematically illustrating a process which iscarried out by a moving object detector section in this embodiment;

FIG. 3 is a flowchart schematically illustrating a process which isperformed by a macro-block determining section in this embodiment;

FIG. 4 is a flowchart schematically illustrating a process of updatingthe contents of a background memory in this embodiment;

FIG. 5 is a flowchart schematically illustrating a process which iscarried out by a moving object determining section in this embodiment;

FIG. 6 is a flowchart schematically illustrating a noise cancelingprocess which is performed in the moving object determining section inthis embodiment;

FIG. 7 is a flowchart schematically illustrating a moving objectenclosing process which is performed in the moving object determiningsection in this embodiment;

FIG. 8 is a flowchart schematically illustrating the moving objectenclosing process which is performed in the moving object determiningsection in this embodiment;

FIG. 9 is a flowchart schematically showing the moving object enclosingprocess which is performed in the moving object determining section inthis embodiment;

FIG. 10 is a flowchart schematically showing the moving object enclosingprocess which is performed in the moving object determining section inthis embodiment;

FIG. 11 is a flowchart schematically showing the moving object enclosingprocess which is performed in the moving object determining section inthis embodiment;

FIG. 12 is a diagram exemplifying the result of decision made by themoving object determining section in this embodiment;

FIG. 13 is a flowchart schematically illustrating a process which isperformed by a moving object combination display in this embodiment; and

FIG. 14 is a diagram exemplifying the result of the display made by themoving object combination display in this embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating the structure of a video movingobject detecting apparatus according to one embodiment of thisinvention. This video moving object detecting apparatus comprises avideo decoder section 100 and a moving object detector section 200,which will be discussed below in order. The following description isgiven of the case where this invention is adapted to a video movingobject detecting apparatus based on the MPEG system and a unit area of areconstructed video signal is equivalent to a macro-block in the MPEGsystem.

Video Decoder Section 100

The video decoder section 100 is a video decoder based on, for example,the MPEG system, or a so-called MPEG decoder. Encoded data which isobtained by compression-encoding in a video encoder (not shown), such asan MPEG encoder, is input to the video decoder section 100 over atransmission channel or via a storage system.

The input encoded data is temporarily stored in an input buffer 101. Theencoded data read out from the input buffer 101 is demultiplexed frameby frame based on a syntax by a demultiplexer section 102, and is theninput to a variable length codes decoder 103. The variable length codesdecoder 103 decodes individual syntax information, such as quantized DCTcoefficient information, mode information and motion vector information,which have undergone variable-length encoding, macro-block bymacro-block. In the following description, a macro-block or a unit areawhich is to be processed is called “interest macro-block”.

The mode for the interest macro-block in the variable length codesdecoder 103 is an INTRA (intra-frame encoding) mode, a mode switch 109is set off in accordance with mode information output from the variablelength codes decoder 103. In this case, the quantized DCT coefficientinformation decoded by the variable length codes decoder 103 isdequantized by a dequantizer 104 and is then subjected to inversediscrete cosine transform (IDCT) in an IDCT section 105, thus yielding areconstructed video signal. This reconstructed video signal is stored asa reference picture signal in a frame memory 107 and is input to amoving object combination display 207 in the moving object detectorsection 200 both via an adder 106. When the mode for the interestmacro-block is an INTER (inter-frame encoding) mode and NOT_CODED(not-encoded block) mode, the mode switch 109 is set on in accordancewith mode information output from the variable length codes decoder 103.In this case, the quantized DCT coefficient information for a predictiveerror signal, decoded by the variable length codes decoder 103, isdequantized by the dequantizer 104 and is then subjected to inversediscrete cosine transform in the IDCT section 105, thus yielding apredictive error signal.

Based on motion vector information decoded in the variable length codesdecoder 103, a motion compensation section 108 performs motioncompensation on the reference picture signal from the frame memory 107.The compensated reference picture signal and the predictive error signalfrom the IDCT section 105 are added by the adder 106, thus producing areconstructed video signal. This reconstructed video signal is stored asthe reference picture signal in the frame memory 107 and is input to themoving object combination display 207 in the moving object detectorsection 200.

Moving Object Detector Section 200

The moving object detector section 200 comprises a macro-blockdetermining section 201, a first cross correlation calculator 202, afirst cross correlation calculator 202, a moving object determiningsection 203, a second cross correlation calculator 204, a backgroundmemory 205, an update switch 206 and the moving object combinationdisplay 207.

The macro-block determining section 201, the moving object determiningsection 203 and the moving object combination display 207 in the movingobject detector section 200 respectively execute three processes,namely, a macro-block determining process (step S101) of determiningwhether an interest macro-block is a background macro-block or anon-background macro-block frame by frame, a moving object determiningprocess (step S102) of determining a moving object based on the resultof the macro-block determining process and a moving object combinationdisplay process (step S103) of combining the determined moving objectwith the decoded reconstructed video signal and displaying the result.

The macro-block determining section 201 determines whether a videosignal represents a background area or a non-background area,macro-block by macro-block in a frame, based on a cross correlationvalue between the reconstructed video signal output from the adder 106and the reference picture signal of one preceding frame held in theframe memory 107, which is acquired by the first cross correlationcalculator 202, and a cross correlation value between the reconstructedvideo signal output from the adder 106 and a background video signalheld in the background memory 205, which is acquired by the second crosscorrelation calculator 204.

The background video signal held in the background memory 205 is updatedwith the reconstructed video signal via the background-memory updateswitch 206 which is set on or off in accordance with the result of thedecision made by the macro-block determining section 201.

Macro-block Determining Process S101

Specific procedures of the macro-block determining process S101 in FIG.2 will be described below with reference to the flowchart illustrated inFIG. 3. In FIG. 3, “i” and “j” respectively represent the vertical andhorizontal macro-block addresses, and V_NMB and H_NMB respectivelyrepresents the numbers of vertical and horizontal macro-blocks in aframe. M[i][j] is a two-dimensional array which stores information aboutwhether each macro-block is a background macro-block or a non-backgroundmacro-block, TRUE indicating a non-background macro-block while FALSEindicates a background macro-block.

First, the macro-block determining section 201 sets the initial value ofthe two-dimensional array M[i][j] to FALSE (step S200). Next, themacro-block determining section 201 determines mode information MODEfrom the variable length codes decoder 103 macro-block by macro-block(step S203).

If the result of the decision in step S203 shows that the modeinformation MODE of the interest macro-block is CODED (encoded block),the macro-block determining section 201 computes a cross correlationvalue between the reconstructed video signal of the encoded macro-blockacquired via the adder 106 and the reference picture signal of onepreceding frame held in the frame memory 107, and the macro-blockdetermining section 201 compares this cross correlation value with athreshold value TH1 (step S204).

If the cross correlation value computed by the first cross correlationcalculator 202 is greater than the threshold value TH1, the macro-blockdetermining section 201 determines that the interest macro-block is anon-background macro-block and sets the two-dimensional array M[i][j] toTRUE (step S208). If the cross correlation value computed by the firstcross correlation calculator 202 is equal to or smaller than thethreshold value TH1, the flow goes to step S206 to further determinewhether the interest macro-block is a background macro-block or anon-background macro-block.

If the result of the decision in step S203 shows that the modeinformation MODE of the interest macro-block is NOT_CODED (encodingunnecessary), on the other hand, the macro-block determining section 201then determines whether the result of the decision on the macro-block ofone preceding frame at the same position as the interest macro-block isa background macro-block, i.e., if the two-dimensional array M[i][j] isFALSE (step S205). If the result of the decision in this step S205 showsthat the macro-block of one preceding frame at the same position as theinterest macro-block is a background macro-block, the macro-blockdetermining section 201 determines the interest macro-block as abackground macro-block and sets the two-dimensional array M[i][j] toFALSE (step S209).

If the result of the decision in this step S205 shows that themacro-block of one preceding frame at the same position as the interestmacro-block is not a background macro-block, on the other hand, it isthen checked if a background video signal corresponding to the positionof the interest macro-block is located in the background memory 205(step S206).

If the background video signal corresponding to the position of theinterest macro-block is not located in the background memory 205, themacro-block determining section 201 determines the interest macro-blockas a new background macro-block and proceeds to step S209. If thebackground video signal corresponding to the position of the interestmacro-block is located in the background memory 205, however, the secondcross correlation calculator 204 calculates a cross correlation valuebetween the video signal of the interest macro-block and the backgroundvideo signal at the position corresponding to the interest macro-blockin the background memory 205, and the macro-block determining section201 compares this cross correlation value with a threshold value TH2(step S207).

If the cross correlation value computed by the second cross correlationcalculator 204 is greater than the threshold value TH2, the macro-blockdetermining section 201 determines that the interest macro-block is anon-background macro-block and sets the two-dimensional array M[i][j] toTRUE (step S208). If this cross correlation value is not more than thethreshold value TH2, the interest macro-block is determined as abackground macro-block and the flow goes to step S209. With regard tothe interest macro-block that has been determined as a backgroundmacro-block, the background video signal at the position correspondingto the interest macro-block in the background memory 205 is updated(step S210).

According to this embodiment, normalized cross correlation values arecomputed by the first and second cross correlation calculators 202 and204 as one example. The normalized cross correlation values are acquiredby the following equation.$C = {\frac{1}{N}{\sum\limits_{i = 0}^{15}\quad{\sum\limits_{j = 0}^{15}\quad( {\frac{{F_{c}( {i,j} )} - \mu_{c}}{\sigma_{c}} - \frac{{F_{r}( {i,j} )} - \mu_{r}}{\sigma_{r}}} )^{2}}}}$where F_(c)(i, j) is the luminance of each pixel of the reconstructedvideo signal of the interest macro-block and F_(r)(i, j) is theluminance of each pixel of a macro-block at the same position as theframe that is to undergo cross correlation computation. μ_(c), μ_(r),σ_(c), σ_(r) are the averages of the luminance of each pixel and thestandard deviations in the respective macro-blocks.

In computing a cross correlation value between the reconstructed videosignal output from the adder 106 in the first cross correlationcalculator 202 and the reference picture signal of one preceding frameheld in the frame memory 107, this cross correlation value may becomputed directly but may be acquired by computing the absolute sumΣ|MV| of the motion vector of the interest macro-block and the absolutesum Σ|COF| of the DCT coefficient from the motion vector information andDCT coefficient information from the variable length codes decoder 103and then comparing the absolute sums with respective threshold values.In this case, when the absolute sum Σ|MV| of the motion vector and theabsolute sum Σ|COF| of the DCT coefficient are greater than theirthreshold values, the interest macro-block is determined as anon-background macro-block. Background Memory Update Step S210

The flowchart shown in FIG. 4 illustrates a process in the backgroundmemory update step S210 in FIG. 3. Referring to FIG. 4, F_(c)(i, j)represents the luminance of each pixel of the reconstructed video signalof the interest macro-block and B(i, j) represents the luminance of eachpixel of the background video signal in the background memory 205.

First, it is determined whether or not the background video signal ofthe macro-block at the same position as the interest macro-block hasalready been written in the background memory 205 (step S701). When thisbackground video signal has already been written in the backgroundmemory 205, the luminance F_(c)(i, j) of each pixel of the reconstructedvideo signal of the interest macro-block is weighted with a weightingfactor w (a real number not less than 0 and equal or smaller than 1) andits weighted mean is added to B(i, j) in the background memory 205 (stepS704) in the loop of steps S702 to S706.

When the background video signal of the macro-block at the same positionas the interest macro-block has not been written in the backgroundmemory 205, on the other hand, the reconstructed video signal F_(c)(i,j) of the interest macro-block is written in F_(c)(i, j) in thebackground memory 205 (step S709) in the loop of steps S707 to S711.

Moving Object Determining Process S102

Specific procedures of the moving object determining process S102 inFIG. 2 will be described below with reference to the flowchartillustrated in FIG. 5. The moving object determining section 203determines a moving object from the result of macro-block-by-macro-blockdetermination on a background macro-block/non-background macro-blockfrom the first cross correlation calculator 202. As shown in FIG. 5, themoving object determining process includes a noise canceling process(step S301) and a moving object enclosing process (step S302).

In the noise canceling process S301, a non-background macro-block eightmacro-blocks around which are all still is considered as noise and isremoved in order to prevent the interest macro-block from beingerroneously detected as a non-background macro-block due to fluctuationof a small object in the background video signal or noise generated atthe time of picking up an object.

The moving object enclosing process S302 detects the smallest rectanglethat encloses an area where non-background macro-blocks are presentadjacent to one another (i.e., an area where a plurality ofnon-background macro-blocks are linked) or the smallest rectangle thatencloses a moving object from the result of determination on abackground macro-block/non-background macro-block after noise has beenremoved in the noise canceling process S301.

Noise Canceling Process S301

The flowchart shown in FIG. 6 illustrates specific procedures of thenoise canceling process S301 in FIG. 5. In FIG. 6, as in FIG. 3, “i” and“j” respectively represent the vertical and horizontal macro-blockaddresses, and V_NMB and H_NMB respectively represents the numbers ofvertical and horizontal macro-blocks in a frame. The two-dimensionalarray M[i][j] stores information about whether each macro-block is abackground macro-block or a non-background macro-block; TRUE indicates anon-background macro-block while FALSE indicates a backgroundmacro-block.

First, the two-dimensional array M[i][j] which is the result of thebackground determination for each macro-block is checked through stepsS401 and S402 (step S403). When the value of the two-dimensional arrayM[i][j] is FALSE or the interest macro-block is a backgroundmacro-block, nothing will be done for that macro-block and the processgoes to the next macro-block.

When the value of the two-dimensional array M[i][j] is TRUE or theinterest macro-block is a non-background macro-block, the results of thebackground determination for eight macro-blocks around that macro-blockare checked (step S405). If all the eight macro-blocks have resulted inFALSE or they are background macro-blocks, that interest macro-block isdetermined as noise and is rewritten to a background macro-block (stepS406). If any of the eight macro-blocks has resulted in TRUE, theinterest macro-block is not determined as noise and the process goes tothe next macro-block. Note that macro-blocks outside the screen areassumed as background macro-blocks.

Moving Object Enclosing Process S302

FIGS. 7 through 11 present flowcharts which illustrate specificprocedures of the moving object enclosing process S302 in FIG. 5. In theflowcharts, n is a counter value indicating the number of movingobjects. S1 to S4 are parameters that indicate the range for searchingfor a rectangle which encloses a moving object. S1 and S2 are theinitial point and end point of the vertical address and S3 and S4 arethe initial point and end point of the horizontal address.

As shown in FIG. 7, first, initialization is performed (step S501) todesignate the entire frame as a search range. Next, a functionRectangular is called to search for the smallest rectangle that enclosesa moving object in the designated search range (step S502).

FIGS. 8 to 11 illustrate the process contents of the functionRectangular. The function Rectangular takes, as inputs, the searchranges S1-S4, the number of moving objects n and the two-dimensionalarray M[i][j] where the results of the background determination for theindividual macro-blocks are stored, and has, as outputs, one-dimensionalarrays B1-B4 where the addresses of a rectangle as the search resultsare stored and the number of moving objects n.

A one-dimensional array HV is a work array for generating a histogramfor the number of non-background macro-blocks in the vertical direction,and a one-dimensional array HH is a work array for generating ahistogram for the number of non-background macro-blocks in thehorizontal direction. A variable VFLAG is a flag which is set to TRUEwhen the value of the horizontal histogram is not 0 and to FALSE whenthis value is 0. A variable HFLAG is a flag which is set to TRUE whenthe value of the vertical histogram is not 0 and to FALSE when thisvalue is 0.

First, the ranges of S1 and S2 as the search ranges of the work array HVfor generating a histogram for the number of non-background macro-blocksin the vertical direction are initialized to 0 (step S601). In thedouble loops of LOOP1 and LOOP2 (S602 to S607), the histogram HV[i] forthe number of non-background macro-blocks in the vertical direction inthe search range is generated. Specifically, the value of the result ofthe background determination, M[i][j], for each macro-block is checked(step S604) and if the value is TRUE or the macro-block is anon-background macro-block, HV[i] is incremented by 1 (step S605),whereas if the value is FALSE, nothing will be done.

Next, the vertical histogram HV[i] generated in the above-describedmanner is searched for a non-zero continuous portion. First, the flagVFLAG is set to FALSE (step S608).

Then, it is checked if the histogram HV[i] is not 0 and the flag VFLAGis FALSE in the order of the search range S1 to the search range S2(step S610). The portion that satisfies this condition is the portion ofthe initial point of a non-zero continuous portion in the histogramHV[i]. Therefore, this portion becomes a candidate for the verticalinitial point of the rectangle to be searched, so that an address i isstored in the one-dimensional array B1[n] and the flag VFLAG is set toTRUE (step S611).

Next, it is checked if the histogram HV[i] is 0 or the end point of thesearch range and the flag VFLAG is TRUE (step S612). The portion thatsatisfies this condition is the portion of the end point of a non-zerocontinuous portion in the histogram HV[i]. Therefore, this portionbecomes a candidate for the vertical end point of the rectangle to besearched, so that if the histogram HV[i] is 0, an address i−1 is storedin the one-dimensional array B2[n] (step S614), and the address i isstored in the one-dimensional array B2[n] otherwise (step S615). Then,the flag VFLAG is set again to FALSE (step S611).

Next, the search ranges S3 and S4 for the work array HH for generating ahistogram HH[i] for the number of non-background macro-blocks in thehorizontal direction are initialized to 0 (step S617). In the nextdouble loops of LOOP4 and LOOP5 (S618 to S623), the histogram HH[i] forthe number of non-background macro-blocks in the horizontal direction inthe search range is generated. Specifically, the value of the result ofthe background determination, M[i][j], for each macro-block is checked(step S604) and if the value is TRUE or the macro-block is anon-background macro-block, HH[i] is incremented by 1 (step S605),whereas if the value is FALSE, nothing will be done.

Next, the generated horizontal histogram HH[i] is searched for anon-zero continuous portion. First, the flag HFLAG is set to FALSE (stepS624).

Then, it is checked if the histogram HH[i] is not 0 and the flag HFLAGis FALSE in the order of the search range 53 to the search range S4(step S626). The portion that satisfies this condition is the portion ofthe initial point of a non-zero continuous portion in the histogramHH[i]. Therefore, this portion becomes a candidate for the horizontalinitial point of the rectangle to be searched, so that an address j isstored in the one-dimensional array B3[n] and the flag HFLAG is set toTRUE (step S627).

Next, it is checked if the histogram HH[i] is 0 or the end point of thesearch range and the flag HFLAG is TRUE (step S628). The portion thatsatisfies this condition is the portion of the end point of a non-zerocontinuous portion in the histogram HH[i]. Therefore, this portionbecomes a candidate for the horizontal end point of the rectangle to besearched, so that if the histogram HH[i] is 0, an address j−1 is storedin the one-dimensional array B4[n] (step S630), and the address j isstored in the one-dimensional array B4[n] otherwise (step S631). Then,the flag HFLAG is set again to FALSE (step S632).

As the search based on the vertical histogram HV[i] and the horizontalhistogram HH[i] is completed, it is then checked if the search resultsB1[n] to B4[n] coincide with the search ranges S1 to S4 (step S633). Ifthere is a match, no further search is necessary and it is determinedthat the smallest rectangle has been acquired (step S634). Then, nrepresenting the number of moving objects is incremented by 1 (stepS635) and the process goes to a search for the next moving object.

If the search results B1[n] to B4[n] do not coincide with the searchranges S1 to S4, a plurality of moving objects are still present in therange of the search results, so that the search results B1[n] to B4[n]are set to the search ranges S1 to S4 (step S636) and the functionRectangular is called again (step S637).

FIG. 12 exemplifies the result of decision made by the moving objectdetermining section 203 in the above-described procedures. In thisexample, two moving objects are determined. The determination resultsshow that the origin of the addresses of the macro-blocks is on theupper left of the frame and moving objects are determined in the layoutof B1[0] to B4[0] and B1[1] to B4[1] as shown in FIG. 12.

Moving Object Combination Display Process S103

FIG. 13 illustrates specific procedures of the moving object combinationdisplay process S103 in FIG. 2. The second cross correlation calculator204 generates a video image which is obtained by combining informationindicating the area of an moving object determined by the moving objectdetermining section 203 and the reconstructed video signal. In thisdiagram, n indicates the number of moving objects in the frame that isacquired by the moving object determining section 203. As B1[i] to B4[i]represent macro-blocks at the four corners of each moving object, arectangle enclosing the moving object is drawn with a white line and iscombined with a reconstructed video image (step S602).

FIG. 14 exemplifies the video image that is produced and displayed bythe moving object combination display 204 in that manner. White linesare so displayed as to enclose two moving objects (persons in thisexample) present in the reconstructed video.

Although a line enclosing the area of an moving object is displayed onthe display screen for the reconstructed video signal in this example asinformation that indicates the area of the moving object, the entirearea of a moving object may be displayed in a different color anddifferent luminance from those of the other area to distinguish themoving object. Any display method may be taken as long as the area of amoving object is distinguishable from the other area. This invention canbe modified in other forms.

As apparent from the foregoing description, this invention can detect amoving object in motion video fast, reliably and accurately.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A video moving object detecting method comprising the steps of: a.determining whether a video signal in a predetermined unit arearepresents a background area or a non-background area from areconstructed video signal acquired by decoding encoded data obtained bycompression-encoding a motion video signal, including determiningwhether an interest macro block used as a unit area is a backgroundmacro block corresponding to the background area or a non-backgroundmacro block corresponding to the non-background area every frame; and b.detecting adjacent unit areas representing the non-background area usinga determination result of the step a to determine the adjacent unitareas as an area of a moving object, including detecting adjacentinterest macro blocks representing the non-background macro block as thearea of the moving object; wherein the step a includes determining abackground or a non-background every macro block in the frame on thebasis of decoded mode information, a first cross correlation valuebetween a local decoded picture signal and a reference picture signal ofa frame preceding by one frame, and a second cross correlation valuebetween the local decoded picture signal and a background picture signalpreceding by one frame.
 2. The method according to claim 1, wherein thestep a includes determining the interest macro block as a backgroundmacro block when the first cross correlation value is larger than afirst threshold.
 3. The method according to claim 1, wherein the step aincludes determining the interest macro block as a non-background macroblock when the second cross correlation value is larger than a secondthreshold, and as a background macro block when the second crosscorrelation value is not more than the second threshold.